In the production of carbon fibers and such, fiber bundles made of a polyacrylonitrile type polymer and such are used as raw threads. These fiber bundles need to have excellent strength and high degree of orientation. Such a fiber bundle, for example may be obtained by spinning a yarn raw solution containing a polyacrylonitrile polymer to form, a solidified fiber, which is then drawn in a bath, followed by drying to densify, thereby obtaining a fiber bundle, which is then subjected to a secondary drawing process carried out under a pressure steam atmosphere.
For the treatment of the fiber bundle under a pressure steam environment, a treatment apparatus is used which makes fiber bundles run inside thereof and supplies pressure steam to the fiber bundle. In such a treatment apparatus, there was the case where the pressure, temperature and humidity in the apparatus became unstable, causing the raise of fuzz on the fiber bundle and fiber bundle breakage, if the pressure steam supplied to the inside of the apparatus leaked in a large amount externally from the inlet and outlet of the pressure steam treatment apparatus. Also, a large amount of pressure steam is required to suppress the influence of the leakage of steam from the apparatus, leading to increase in energy cost.
As a treating apparatus that restrains the leakage of pressure steam from the inside of the apparatus, a pressure steam treating apparatus is known which is provided with a pressure steam treating section for treating fiber bundles running in a fixed direction and two labyrinth sealing chambers extending from the front and back of the pressure steam treating section. The above labyrinth sealing chambers were each provided with a plurality of labyrinth nozzles made of plate fragments extending at right angle from the internal wall surface thereof to the fiber bundles wherein steam energy is consumed when steam passes through each space (expansion room) between these labyrinth nozzles, to thereby reduce the leak amount of pressure steam.
Specifically, Japanese Patent Application Laid-Open No. 2001-140161 (Patent Document 1) discloses a pressure steam treatment apparatus which is provided with a pressure steam treating section and two labyrinth sealing chambers extending from the front and back of the pressure steam treating section, wherein each labyrinth sealing chamber is provided with labyrinth nozzles in 80 to 120 stages, and the ratio (L/P) of the length L of the labyrinth nozzle extended from the inside wall to the pitch P between adjacent labyrinth nozzles is from 0.3 to 1.2.